Adenosine-sensitive ventricular tachycardia appears to arise from relatively discrete sites predominantly located in the free wall of the pulmonary infundibulum. The localized nature of this tachycardia renders it amenable to long-term cure by catheter ablation techniques.

Previous work has suggested that a comparison of electrograms from two or more sites may best differentiate fibrillatory from nonfibrillatory rhythms. The coherence spectrum is a measure by which two signals may be compared quantitatively in the frequency domain. In the present study, the coherence spectrum was used to quantify the relation between spectral components of electrograms from two sites in either the atrium or ventricle during both fibrillatory and nonfibrillatory rhythms. Bipolar recordings of 35 rhythms from 20 patients were analyzed for coherence in the 1-59 Hz band. The 17 nonfibrillatory rhythms were sinus rhythm (six), paroxysmal supraventricular tachycardia (two), atrial flutter (four), and monomorphic ventricular tachycardia (five). The 18 fibrillatory rhythms were atrial fibrillation (12) and ventricular fibrillation (six). Nonfibrillatory rhythms exhibited moderate-to-high levels of coherence throughout the 1-59 Hz band, with peaks concentrated at the rhythm's fundamental frequency and its harmonics. Fibrillatory rhythms exhibited little coherence throughout the 1-59 Hz band, and harmonics were not evident. The mean magnitude-squared coherence (scale of 0 to 1) for the 1-59 Hz band ranged from 0.22 to 0.86 (mean± SD, 0.52 ±0.19) for nonfibrillatory rhythms and from 0.042 to 0.12 (0.067±0.021) for fibrillatory rhythms. Separation of fibrillatory and nonfibrillatory rhythms was possible whether signals were recorded by floating or fixed-electrode configurations. These findings indicate that comparison of two electrograms with magnitude-squared coherence measurements differentiates fibrillatory from nonfibrillatory rhythms. A recognition algorithm based on coherence spectra may be robust in the face of major variations in lead configuration. Furthermore, the coherence spectra may provide a means to quantify the "organization" or "disorganization" of a cardiac rhythm. (Circulation 1989;80:112-119) F ibrillatory rhythms are typically described as "chaotic" and "disorganized." More specifically, the activity from multiple sites during fibrillation has been described as asynchronous and incoordinate.1-6 Allessie et a16 have suggested that the comparison of activity from two or more sites may best differentiate fibrillatory from nonfibrillatory rhythms. While this "altered spatial arrangement of conduction"7 is quintessential to fibrillation, this qualitative characteristic remains to be quantified. Previous studies have used frequencyFrom the

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To assess whether the level of risk of having significant electrophysiologic abnormalities can be determined, 29 clinical variables were analyzed in 104 patients with unexplained syncope who underwent electrophysiologic testing. A positive electrophysiologic study was defined as: a sinus node recovery time greater than or equal to 3 seconds; HV interval greater than or equal to 100 ms; infranodal block during atrial pacing; unimorphic ventricular tachycardia; and supraventricular tachycardia associated with hypotension. Thirty-one patients had a positive study, with inducible ventricular tachycardia being the most common finding (71% of positive studies). A left ventricular ejection fraction less than or equal to 0.40 was the most powerful predictor of a positive electrophysiologic study (p less than 0.00001), followed by the presence of bundle branch block (p less than 0.00003), coronary artery disease (p less than 0.0003), remote myocardial infarction (p less than 0.00006), use of type 1 antiarrhythmic drugs (p less than 0.00003), injury related to loss of consciousness (p less than 0.01) and male sex (p less than 0.01). A negative electrophysiologic study was associated with an ejection fraction greater than 0.40 (p less than 0.00001), the absence of structural heart disease (p less than 0.00001), a normal electrocardiogram (ECG) (p less than 0.0001) and normal ambulatory ECG monitoring (p less than 0.0001). The probability of a negative study increased as the number and duration of syncopal episodes increased.(ABSTRACT TRUNCATED AT 250 WORDS)

In eight patients, the right ventricular effective refractory period, rate-dependent changes in intraventricular conduction (as reflected by QRS duration during ventricular paced cycle lengths of 600 to 250 ms) and results of programmed ventricular stimulation were determined in the control state, 5 minutes after the intravenous infusion of 10 mg/kg body weight of amiodarone and after 2 months of treatment with oral amiodarone. The right ventricular effective refractory period was 230 +/- 30 ms (mean +/- SD) in the control study, 248 +/- 27 ms after intravenous amiodarone (p less than 0.001) and 296 +/- 26 ms after oral amiodarone (p less than 0.001). In the control state, QRS duration was constant at all paced cycle lengths. Intravenous amiodarone resulted in a rate-dependent prolongation of QRS duration. This rate-dependent prolongation was markedly accentuated by oral amiodarone in six patients who had an elevated serum level of reverse triiodothyronine (T3) after 2 months of oral treatment, but it was not more pronounced than the effects of intravenous amiodarone in two patients with a normal reverse T3 serum level after oral therapy. Both intravenous and oral amiodarone either suppressed or modified the induction of ventricular tachycardia by programmed stimulation in some patients, but in a discordant fashion. The relative effects of intravenous and oral amiodarone on ventricular refractoriness and conduction and on ventricular tachycardia induction did not correlate with serum amiodarone levels. Chronic amiodarone therapy results in a marked prolongation in ventricular refractoriness compared with the relatively small but significant increase that occurs after intravenous amiodarone.(ABSTRACT TRUNCATED AT 250 WORDS)